With the drastic development of society since the 20th century, the supply and demand for energy has become unstable and environmental problems such as global warming have come to the fore, and thus attempts to use a type of fossil energy which is environmentally friendly continue, and thorough research into manufacturing processes for producing fuel that never causes environmental pollution is ongoing. Particularly instead of the direct combustion of coal, which causes severe environmental pollution, efforts are being made to convert coal into a gas fuel such as synthetic gas (which is a mixture comprising hydrogen, carbon monoxide, etc.), which is called gasification.
That is, the term gasification means that solid/liquid fuel including carbon as a basic component, such as coal, petroleum coke, biomass, etc., reacts with a gas such as oxygen, Steam, carbon dioxide, and hydrogen, thus producing combustible gases such as CO, H2 and CH4. This process is mainly carried out under conditions of high temperature and high pressure in order to maximize gasification capacity and efficiency, and the produced combustible gases are used as fuel gas for power generation or as feedstock for chemical products or synthetic petroleum via a methanol synthesis process, an NH3 Synthesis process and a Fischer-Tropsch synthesis process, or hydrogen is maximally produced and utilized as a hydrogen source in the hydrothreating and the hydrocracking of crude oil.
A typical gasification system enables coal or other carbon-containing materials to react with steam and oxygen (or air) to produce a synthetic gas composed mainly of hydrogen and carbon monoxide.
FIG. 1 schematically shows a conventional gasification process. CTL (Coal-to-Liquids) using the conventional gasification process is described below.
Specifically, Steam, oxygen and coal are fed into a gasifier. The fed coal reacts with H2O and oxygen in the gasifier, thus generating a product including H2, CO, CO2, etc. The reactions in the gasifier are as follows.C+H2O→CO+H2 C+CO2→2COC+O2→CO2 
The product generated in the gasifier is subjected to removal of particulate materials, Hg and NOx and then removal of acid gas to eliminate H2S and CO2. Subsequently, the produced gases are selectively subjected to the water-gas shift process like that below so that they are used for F-T synthesis reaction or MeOH synthesis reaction, and the remaining H2 is used alone.
<Water-Gas Shift Reaction>CO+H2O→H2+CO2 
<F-T Reaction>CO+2H2→—(CH2)n—+H2O
<Methanol (MeOH) Synthesis>CO+2H2→CH3OH
In the case where such a typical steam/oxygen gasifier is used, carbon gasification (C+H2O→H2+CO or C+CO2→2CO) is very highly endothermic, and thus the heat value corresponding thereto should be supplied by the combustion reaction of carbon (C+O2→CO2). Hence, part of the hydrocarbon used as the feed is converted into carbon dioxide following combustion inside or outside the gasifier. After gasification, in the case where the synthetic gas generated from the gasifier is subjected to a water-gas shift process so that the ratio of H2/CO in a synthetic gas that is stoichiometrically required for F-T synthesis or methanol production is set to 2, the theoretical carbon efficiency of the overall process is less than 49.8%, and the generation of CO2 is calculated to be 0.502 mol CO2/mol C or more. Here, the following definition of carbon efficiency is used.Carbon efficiency(%)=(mol of CO in synthetic gas having H2/CO of 2˜2.1)×100/mol of carbon of gasification feed
Gasification1.0C + 1.0H2O --> 1.0H2 + 1.0COCombustion0.34C + 0.34O2 --> 0.34CO2Water-gas Shift0.33CO + 0.33H2O --> 0.33H2 + 0.33CO2Overall Reaction1.34C + 1.33H2O + 0.34O2 --> 1.33H2 + 0.67CO +0.67CO2
Such low carbon efficiency decreases the profitability of CTL (Coal-to-Liquids). Also in order to reduce the generation of greenhouse gas CO2, there is a need for an additional and very expensive facility in order to capture and store CO2, making it difficult to construct profitable commercial plants.
Korean Patent Publication No. 2008-0041635 discloses an alkali metal catalytic steam gasification method using a CO2 trap material and/or a mineral binder material in a gas generator. In order to increase the activity of the catalyst in the above patent, the CO2 trap material for forming CO2 into solid carbonate or bicarbonate is used but CO2 cannot be converted into actually usable materials such as CO or the like. Furthermore, the above patent is problematic because a specific catalyst is used and a CO2 trap material such as CaO or the like is additionally required.